Liquefied petroleum gas filtration system

ABSTRACT

Described herein are filter assemblies for removing high molecular weight organic components from liquefied petroleum gas, as well as methods for removing high molecular weight components from liquefied petroleum gases. The filter assemblies include an upstream carbon-containing filter media pack and a downstream filter media pack.

This application claims the benefit of U.S. Provisional Application No.61/489,938, filed May 25, 2011, the contents of which are hereinincorporated by reference.

FIELD OF THE INVENTION

The invention described herein relates to a filtration system. Inparticular, the invention relates to a filtration system for the removalof high molecular weight organic compounds from liquefied petroleum gas.

BACKGROUND OF THE INVENTION

Crude oil contains many different hydrocarbon compounds. The majorcompounds include petroleum gas, which includes small alkanes andalkenes (C₁-C₄), such as methane, ethane, propane, propylene, butane,and butylene; naphtha, which includes intermediate hydrocarbons (C₅-C₉);kerosene, a liquid mixture of C₁₀-C₁₈ alkanes and aromatics; diesel oil,which includes liquid alkanes containing twelve or more carbon atoms;lubricating oil, which includes long chain (C₂₀-C₅₀) alkanes,cycloalkanes, and aromatics; and fuel oil, which includes long chain(C₂₀-C₇₀) alkanes, cycloalkanes, and aromatics, along with various solidresiduals such as coke, asphalt, tar, and waxes. The various hydrocarboncompounds are typically separated by fractional distillation.

Liquefied petroleum gas (also called LPG) refers to a flammable mixtureof C₁-C₄ hydrocarbons that exists as a liquid at or below about −42° C.,or when stored under pressure. At atmospheric pressure and temperaturesabove about −42° C., LPG is a colorless and odorless gas. As withnatural gas, an identifying odorant, such as ethyl mercaptan, istypically added so that leaks of LPG can be more easily detected. SinceLPG is substantially more compact as a liquid than as a gas, it istypically stored and transported under pressure (about 1725 kilopascals)where it exists as both a liquid and vapor.

Some LPG fuel systems include a filter to remove small particulatematerial from the fuel. However, a brown greasy or waxy material canstill build up in the fuel system, for example, in the vaporizer(sometimes called a converter), downstream in the vapor hose, in thecarburetor, and in the valves or mixer. The build-up is due to traceamounts of high molecular weight materials (also called greases, waxesor heavies) in the LPG acquired during refining, distribution and/orstorage. When the LPG is vaporized, these high molecular weightmaterials can precipitate out of the vapor stream, often resulting indeposits that can obstruct injectors, valves, vaporizers or othercomponents and can interfere with the operation of the fuel system. Thiscan result in additional maintenance, shutdowns, and increased costs.

Therefore, a need exists for a system that can reduce the deposit ofhigh molecular weight materials on LPG fuel system components whilestill removing particulate contaminants.

SUMMARY OF THE INVENTION

Described herein are filter assemblies for removing high molecularweight organic components from liquefied petroleum gas, as well asmethods for removing high molecular weight components from liquefiedpetroleum gases. The filter assemblies can include, in someimplementations, two separate filter media packs: A first filter mediapack is configured to remove high molecular weight compounds fromliquefied petroleum gases. This first filter media pack is typicallyconfigured so that even after it reaches capacity for holding highmolecular weight compounds, liquefied petroleum gases can still readilypass through the filter media. This first filter media pack isconfigured to readily load significant quantities of high molecularweight contaminants without excessive restriction of flow upon reachingcapacity. The second filter media pack, which is positioned downstreamfrom the first media pack, is also configured to load high molecularweight contaminants, although typically significantly lower quantitiesthan the first media pack. However, unlike the first media pack, thesecond media pack is generally configured to have a very significantincrease in restriction of flow upon loading with high molecular weighthydrocarbons. Thus, unlike the first media pack, in certain embodimentsthe downstream media pack significantly restricts flow of the liquefiedpetroleum gas once the downstream media pack has loaded with highmolecular weight contaminants. In particular, once the downstream mediapack has loaded to near theoretical capacity with high molecular weightcontaminants it provides a significant resistance to fluid flow. As usedherein, theoretical capacity refers to the total change in mass of thefilter media pack upon prolonged exposure to LPG containing highmolecular weight hydrocarbons. Generally such capacity is measured atthe saturation point of the media, which is where the quantity ofadsorbed and retained high molecular weight hydrocarbons is no longerincreasing. In practice the media may continue to very gradually pick upsmall quantities of high molecular weight hydrocarbons once itapproaches saturation, and therefore another capacity measure is“functional capacity”. Functional capacity is the point where saturationof the media is substantially reached, where the pickup of contaminantstypically has slowed down dramatically, and where high molecular weightcontaminants readily pass through the filter media. Thus, functionalcapacity is reached at the point were significant contaminantbreakthrough occurs. Functional capacity is generally not materiallydifferent than the theoretical capacity. In fact, the two are often verysimilar. However, the term “functional capacity” can be used to clarifythat full theoretical capacity is in some regards a hypothetical conceptbecause media can continue to load even trivial, all-but-unmeasurableamounts of contaminants for a long period of time after any functionalbenefit of filtration has diminished completely.

Typically the first filter media pack (the upstream media pack) has amuch higher capacity to retain high molecular weight contaminants thanthe downstream filter media pack. The upstream media pack can includeactivated carbon, such as a packed carbon bed, that has relatively highcapacity for adsorbing and retaining high molecular weight contaminants.The second filter media pack (the downstream media pack) can be formedof a material comprising a fine fiber, such as nanofiber. The downstreammedia pack generally has a relatively low capacity for adsorbing andretaining high molecular weight contaminants relative to the upstreammedia pack, but upon reaching capacity it provides a restriction to flowof liquid through the media pack.

Thus, the upstream media pack performs a primary function of reducingcontaminants in the liquefied petroleum gas. The downstream media pack'sprimary function is to rapidly provide resistance to fluid flow once itis exposed to high molecular weight contaminants due to the performanceof the upstream media pack diminishing. Thus, once the upstream mediapack approaches or reaches capacity, and high molecular weightcontaminants flow through this upstream media pack, the downstream mediapack quickly reaches a point of sufficient loading that fluid flowthrough the filter assembly is meaningfully impeded. This impedance toflow can be measured by a change in pressure differential from theupstream to downstream side of the media packs. In this manner, thedownstream (or second) filter media pack serves as an end of lifeindicator for the filter assembly by restricting flow once the upstream(or first) filter media pack is no longer adequately removing the highmolecular weight contaminants.

In an example embodiment the first filter media pack is configured toexhibit a change in upstream to downstream pressure differential of lessthan 200 percent upon reaching saturation for retaining high molecularweight compounds, and the second filter media pack is configured toexhibit a change in upstream to downstream pressure differential ofgreater than 200 percent upon reaching saturation of high molecularweight compounds. The second filter media pack may be configured toexhibit a change in upstream to downstream pressure differential ofgreater than 400 percent upon reaching saturation of high molecularweight compounds. The first filter media pack can be arranged in an openchannel configuration to further avoid flow restrictions upon reachingcapacity.

In addition, further elements can be added to the assembly. For example,a third media pack can be added to remove particulate contaminants (andalso to optionally remove carbon or other material which has thepotential to bleed from the first filter media pack). The third filtermedia pack can have a mean flow pore size of 10 microns or less, forexample. In some implementations the third filter media pack has anefficiency of at least 99.9 percent for removal of particulatecontaminants having an average particle size of 5 microns. Theparticulate filter can be positioned, for example, upstream of the firstand second filter media packs, between the first and second filter mediapacks, or downstream from both the first and second filter media packs.

In an example embodiment the filter assemblies include an upstreamcarbon-containing filter element and a downstream end-of-life indicatorcomprising a fine fiber web. In one embodiment, the carbon-containingfilter element includes activated carbon derived from wood, coconut orcoal that has a surface area of at least about 500 m²/g and an averagepore size of at least about 20 Angstroms (measured using BET surfaceanalysis, described below, which measures pore volume). The activatedcarbon can be, for example, powdered or granular, or a combinationthereof.

In some implementations the second filter media pack has a totalcapacity for retaining high molecular weight hydrocarbons that is nomore than 5 percent of the total capacity of the first filter media packfor retaining high molecular weight hydrocarbons. The second filtermedia pack can comprise a fine fiber web. Suitable fine fiber websinclude those with a pore size of no more than about 25 microns(measured using scanning electron microscopy analysis, described below).Second filter media packs with a pore size of no more than about 10microns are suitable for some embodiments.

A filter assembly for filtering high molecular weight compounds fromliquefied petroleum gas is also disclosed in which the filter assemblyincludes a first filter media pack configured to remove high molecularweight compounds, the first filter media pack having a first totalcapacity for retaining high molecular weight hydrocarbons; and a secondfilter media pack configured to remove high molecular weight compounds,the second filter media pack located downstream from the first filtermedia pack, the second filter media pack having a second total capacityfor retaining high molecular weight hydrocarbons. The second filtermedia pack has a total capacity for retaining high molecular weighthydrocarbons that is no more than 10 percent of the total capacity ofthe first filter media pack for retaining high molecular weighthydrocarbons, and the second filter media pack demonstrates at least a25 percent increase in resistance to flow of liquefied petroleum gasupon or before reaching total capacity. In some implementations thatincrease in resistance to flow is at least 50 percent, alternatively atleast 100 percent, optionally at least 200 percent, and in otherimplementations at least 400 percent.

Optionally a third filter media pack is positioned intermediate thefirst filter media pack and the second filter media pack, the thirdfilter media pack having an efficiency of at least 99.9 percent forremoval of particulate contaminants having an average particle size of 5microns. The third filter media pack intermediate the first filter mediapack and the second filter media pack can have a mean flow pore size ofless than 10 microns in some embodiments (measured using, for example,an automated air permeability porometer manufactured by PorousMaterials, Inc.).

The first filter media pack can include activated carbon, such asactivated carbon having a surface area of at least about 500 m²/g and anaverage pore size of at least about 20 Angstroms. In someimplementations the second filter media pack has a total capacity forretaining high molecular weight hydrocarbons that is no more than 2percent of the total capacity of the first filter media pack forretaining high molecular weight hydrocarbons, and can have an openchannel configuration. Suitable media for the first filter media packalso includes carbon fibers. The second filter media pack may include afine fiber web, such as a fine fiber web with a pore size of no morethan about 25 microns. Alternatively, the second filter media packcomprises a fine fiber web with a pore size of no more than about 10microns.

Further, a filter assembly for filtering high molecular weight compoundsfrom liquefied petroleum gas is disclosed in which a first filter mediapack is configured to remove high molecular weight compounds such thatinitial efficiency for removal of high molecular weight hydrocarbonsfrom a liquefied petroleum gas is at least 80 percent at high molecularweight hydrocarbon concentrations of up to 0.5 percent by weight. Thefirst filter media pack has a first total capacity for retaining highmolecular weight hydrocarbons. A second filter media pack is configuredto also remove high molecular weight compounds. The second filter mediapack is located downstream from the first filter media pack. The secondfilter media pack has an initial efficiency at removing of highmolecular weight hydrocarbons of at least 80 percent at originalconcentrations of up to 0.5 percent by weight of the liquefied petroleumgas, the second filter media pack having a second total capacity forretaining high molecular weight hydrocarbons that is no more than 10percent of the first total capacity of the first filter media pack. Incertain embodiments the second filter media pack demonstrates anincreased resistance to flow of liquefied petroleum gas of at least 25percent upon or before reaching total capacity.

Methods for determining service life of a filter assembly configured toremove high molecular weight hydrocarbons from liquefied petroleum gasare also disclosed. The methods can use any of the filter assemblies andmedia packs described herein. In an example implementation, the methodincludes providing a first filter media pack and passing liquefiedpetroleum gas through it such that at least 80 percent of initial highmolecular weight hydrocarbons are removed. A second filter media pack islocated downstream from the first filter media pack. When passing theliquefied petroleum gas through the second filter media pack, the secondfilter media pack retains at least 50 percent of remaining highmolecular weight hydrocarbons that have passed through the first mediapack. The second filter media pack has a total capacity for retaininghigh molecular weight hydrocarbons that is no more than 10 percent ofthe total capacity of the first filter media pack, wherein the secondfilter media pack demonstrates an increased resistance to flow ofliquefied petroleum gas of at least 50 percent upon or before reachingtotal capacity.

This summary is an overview of some of the teachings of the presentapplication and is not intended to be an exclusive or exhaustivetreatment of the present subject matter. Further details are found inthe detailed description and appended claims. Other aspects will beapparent to persons skilled in the art upon reading and understandingthe following detailed description and viewing the drawings that form apart thereof, each of which is not to be taken in a limiting sense. Thescope of the present invention is defined by the appended claims andtheir legal equivalents.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in regards to the Figures, in which:

FIG. 1 is a schematic of one embodiment of a filter assembly constructedand arranged in accordance with an implementation of the invention.

FIG. 2 is a cross-sectional view of the filter assembly of FIG. 1 takenalong line 2-2.

FIG. 3 is a cross-sectional view of an alternative filter assemblyconstructed and arranged in accordance with an implementation of theinvention.

FIG. 4A is a schematic of an embodiment of a filter assembly constructedand arranged in accordance with an implementation of the invention.

FIG. 4B is a schematic of an embodiment of a filter assembly constructedand arranged in accordance with an implementation of the invention.

FIG. 5A is a photograph of the interior of regulator assembly in a LPGdistribution device which has been used with unfiltered LPG liquids, theregulator assembly showing a deposit of high molecular weighthydrocarbons.

FIG. 5B is a photograph of the interior of regulator assembly in a LPGdistribution device, which has been used with LPG liquids filtered inaccordance with the teachings herein, the regulator assembly showing novisible deposit of high molecular weight hydrocarbons.

FIG. 6 is a photograph of fine fiber media showing deposits of highmolecular weight hydrocarbons sufficient to substantially cover themedia surface.

FIG. 7 is a photograph of a particulate removal media used for removalof particulates downstream from a carbon filter element, the particulateremoval media showing relatively little loading of high molecular weighthydrocarbons.

FIG. 8 is a chart showing relative pressure drop in various filter mediamaterials that have been exposed to hexane containing high molecularweight contaminants.

FIG. 9 is a chart showing mass gain of various filter media materialsthat have been exposed to hexane containing high molecular weightcontaminants.

FIG. 10 is a chart showing pressure differential in a media uponexposure to liquefied petroleum gas.

While the invention is susceptible to various modifications andalternative forms, specifics thereof have been shown by way of exampleand drawings, and will be described in detail. It should be understood,however, that the invention is not limited to the particular embodimentsdescribed. On the contrary, the intention is to second modifications,equivalents, and alternatives falling within the spirit and scope of theinvention.

DETAILED DESCRIPTION

Described herein is a system for removal of contaminants from liquefiedpetroleum gas (LPG), in particular a filtration system that adsorbs,separates, and/or filters out high molecular weight organic materialsfrom LPG. These high molecular weight organic materials can build-up ina fuel system unless removed.

More particularly, the system described herein removes high molecularweight organics that are acquired through refining, distribution, andstorage. The system reduces build-up of deposits in the LPG fuel systeminjectors, valves, vaporizers or other components. The systems andmethods described herein are suitable for use with a variety of gradesof LPG, including, for example, commercial grade propane; enginefuel-grade propane (also known as HD-5 propane); and commercial gradebutane.

The systems and methods can be used at a variety of locations in the LPGfuel supply chain, under a variety of conditions, including, but notlimited to: oil refinery or natural gas processing plants; duringshipping, including on highway transport trucks (which typically carryfrom about 25,000 to 50,000 liters of LPG) and on smaller bulk deliverytrucks (which typically carry from about 4,000 to 20,000 liters of LPGand dispense LPG at a flow rate from about 75 liters per minute (LPM)),up to about 200 LPM; during storage in “bulk plants” (retail propanestorage facilities); at a dispenser storage tank, for example, a propanetank and/or pump at a service station that is used to fill propanecylinders (which typically dispense LPG at a flow rate of as little asabout 20 LPM, and up to about 50 GPM); or at the point of use, forexample, in the fuel supply on an engine (which can move LPG at a flowrate of as little as 4 liters per hour (LPH), or up to about 40 LPH, orup to 60 LPH.

The contaminants removed by the systems and methods include, but are notlimited to, high molecular weight organic materials, such ashydrocarbons with more than 16 carbon atoms (greater than C₁₆), orbetween about C₂₀ to about C₆₀ or more than about C₆₀. In particular,contaminants which are removed include high molecular weight organicmaterials that are at least partially soluble in LPG.

The systems and methods are capable of adsorbing, separating and/orfiltering out high molecular weight components from LPG, withoutremoving excessive amounts odorant, such as ethyl mercaptan, which isfrequently included in LPG as a safety precaution. In general, ethylmercaptan is added in an amount of at least about 35 ppm and isconsidered non-detectable at levels below 12 ppm. In one embodiment,substantially no mercaptan is removed by the filter system. In otherimplementations less than 50 percent of mercaptan is removed, optionallyless than 25 percent of mercaptan is removed, and desirably less than 10percent of mercaptan is removed.

In one embodiment, the filter system is configured as a single passfilter, for example, a filter used during bulk fill or bulk dispensing.In a more particular embodiment, the filter system can be configured asa cartridge (or replaceable element) filter, in which a permanenthousing contains a replaceable filter element or cartridge. In analternate embodiment, the filter system is configured as a spin-onfilter, in which a self-contained housing and element assembly isunscrewed from its mount, discarded and replaced with a new housing andfilter assembly.

The filter systems can include, in some implementations, two separatefilter media packs: A first filter media pack is configured to removehigh molecular weight compounds from liquefied petroleum gases. Thisfirst filter media is typically configured so that even once it reachescapacity for holding high molecular weight compounds, liquefiedpetroleum gases can still readily pass through the filter media. Thus,this first filter media is configured to readily load significantquantities of high molecular weight contaminants without excessiverestriction of flow upon reaching capacity. The second filter media packis positioned downstream from the first media pack. Unlike the firstmedia pack, in certain embodiments the downstream media packsignificantly restricts flow of the liquefied petroleum gas once thedownstream media pack has loaded with high molecular weightcontaminants. In particular, once the downstream media pack has loadedto near capacity with high molecular weight contaminants it provides asignificant resistance to fluid flow.

Typically the first filter media pack (the upstream media pack) has amuch higher capacity to retain high molecular weight contaminants thanthe downstream filter media pack. The upstream media pack can includeactivated carbon, such as a packed carbon bed, that has relatively highcapacity for adsorbing and retaining high molecular weight contaminants.The second filter media pack (the downstream media pack) can be formedof a material comprising a fine fiber, such as nanofiber. The downstreammedia pack has a relatively low capacity for adsorbing and retaininghigh molecular weight contaminants, but upon reaching capacity itprovides a restriction to flow of liquid through the media pack.

Thus, in use the upstream media pack performs a primary function ofreducing contaminants in the liquefied petroleum gas. The downstreammedia pack's primary function is to rapidly provide resistance to fluidflow as quickly as possible after it is exposed to high molecular weightcontaminants. Thus, once the upstream media pack approaches or reachescapacity, and high molecular weight contaminants flow through thisupstream media pack without being retained, the downstream media packquickly reaches a point of sufficient loading that fluid flow throughthe filter assembly is meaningfully impeded (and potentially completelystopped). In this manner, the downstream (or second) filter media packserves as an end of life indicator for the filter assembly byrestricting flow once the upstream (or first) filter media pack is noadequately removing the high molecular weight contaminants.

In addition, further elements can be added to the assembly. For example,a particulate filter in a third media pack can be added to removeparticulate contaminants (and also to optionally remove carbon or otheradsorbent that is released from the first filter media pack). The thirdfilter media pack can have a mean flow pore size of 10 microns or less,for example. Such pore testing can be accomplished utilizing, forexample, an automated air permeability porometer manufactured by PorousMaterials, Inc., as described in U.S. Patent Publication No.2011/0198280, incorporated herein by reference in its entirety. Theparticulate filter can be positioned, for example, upstream of the firstand second filter media packs, between the first and second filter mediapacks, or downstream from both the first and second filter media packs.

Filter Assembly Configuration

Now, in reference to the drawings, one embodiment of a filter system 18is shown in FIG. 1. Although other configurations are possible, in theembodiment shown in FIG. 1 the filter system includes a filter assembly10 that includes a generally cylindrical housing 14 that defines achamber in which a filter element 12 is positioned. In this embodiment,housing 14 is constructed from a thin-walled material, such as metal orother synthetic material, that is capable of withstanding pressures ofat least about 500 kilopascals, or between about 1000 kilopascals and2000 kilopascals, and up to 3000 kilopascals. In one embodiment, thehousing 14 can be formed from deep drawn steel with a wall thicknessbetween about 0.25 millimeters and 2.5 millimeters, or between about 0.5millimeters and 1.25 millimeters.

In the depicted embodiment, the filter assembly 10 is operably mountedto a filter block or filter head 16, typically by screwing the filterassembly 10 onto the filter head 16 by internal threads on the filterassembly 10. The filter system 18 includes a supply 20 for supplyingfluid to the filter assembly 10 through an inlet 22 of the filter head16. The fluid enters and is filtered by the filter element 12 and exitsthe filter head 16 at an outlet 24 of the filter head 16 and is carriedaway by a passage 26. It will be understood that filter assembly 10 isdepicted in an example configuration, and that numerous otherconfigurations are possible for filter assemblies without deviating fromthe scope of the invention.

FIG. 2 shows a cross-sectional view of the filter assembly 10 of FIG. 1taken along line 2-2, in which the filter element 12 includes agenerally cylindrical filter medium, supported within the canister viaone or more end caps 23, 25 such that unfiltered fluid flows through thefilter medium in a generally radial direction. In the embodiment shownin FIG. 2, the LPG fuel follows an outside/in pattern in which LPG fuelpasses from an outer surface 30 of the filter 12 towards an innersurface 31 of the filter 12, as shown by the arrows marked “F” in FIG.2. However, it also possible to design the filter assembly 18 such thatthe fuel follows an inside/out pattern in which the fuel passes from aninner surface of the filter towards an outer surface of the filter (notshown). In the embodiment shown in FIG. 2, the outer surface 30 is“upstream” and the inner surface 31 is “downstream” with respect to thedirection of the fuel flow.

In an alternative embodiment, shown in FIG. 3, the filter element 18includes multiple layers of carbon-containing filter element 20 andend-of-life indicator layers 22, e.g., anywhere from 2 to 50 layers,wherein each “layer” includes a carbon-containing filter element and anend-of-life indicator layer.

FIG. 4A shows a filter system 180 which includes a primary filter 181and secondary filter 182. The LPG fluid enters the primary filter 181 ofthe system through supply 120. After passing through the primary filter181, the LPG is transported to the secondary filter 182 by conduit 130.Once the LPG crosses the secondary filter 182, it exits the system viapassage 126. In the dual-filter embodiment shown in FIG. 4A, the primaryfilter 181 includes a housing in which a carbon-containing filterelement is located.

The secondary filter 182 includes a housing in which a fine fiber web islocated, wherein the fine fiber web is configured to entrap“breakthrough” high molecular weight organics that are not adsorbed bythe primary filter. As described above, the “breakthrough” highmolecular weight organics form a film on the fiber web, which increasesbackpressure and serves as a fuse to determine end-of-life. If desired,the system can also include one or more downstream particulate filtersconfigured to remove particulates, such as carbon particulates, from theLPG stream.

FIG. 4B shows a filter system 280 which includes a first filter 281, asecond filter 282, and a third filter 283. The LPG fluid enters thefirst filter 281 of the system through supply 220. After passing throughthe first filter 281, the LPG is transported to the second filter 182 byconduit 230. Once the LPG crosses the second filter 282, it passes tothird filter 284 via conduit 227 before exiting the system via passage228. In the filter embodiment shown in FIG. 4B, the filter 281 includesa housing in which a carbon-containing filter element is located, thesecond filter 282 includes a housing in which a particulate fiber islocated, and the third filter 283 includes a housing in which a finefiber web is configured to entrap “breakthrough” high molecular weightorganics that are not adsorbed by the primary filter. As describedabove, the “breakthrough” high molecular weight organics form a film onthe fiber web, which increases backpressure and serves as a fuse todetermine end-of-life.

FIG. 5A and FIG. 5B shows photographs of the interior of an LPG handlingassembly after prolonged exposure to liquefied petroleum gases. In FIG.5A, the liquefied petroleum gas has not been filtered using an assemblyas described herein. In FIG. 5B the liquefied petroleum gas has beenfiltered using an assembly as described herein. Deposits of contaminantmaterials, identified as high molecular weight hydrocarbons, have formedin assembly. Such deposits eventually become so significant so as todiminish performance of the regulator, and can ultimately fully obscurefuel flow paths.

Upstream Adsorbent Material

A variety of adsorbent materials are suitable for the upstream adsorbentmedia pack. In particular, carbon containing filter elements aresuitable for use in the system of the invention. In general, acarbon-containing filter element containing carbon media with a highsurface area and an open pore structure, such as activated carbon, iseffective for adsorbing high molecular weight organic impurities fromLPG.

In general, LPG that includes more than about 0.25% volume/volume highmolecular weight organic impurities is unusable. The systems and methodsdisclosed herein can reduce such impurities to acceptable levels. LPGwith less than about 0.05% volume/volume high molecular weight organicimpurities is desirable. In one embodiment, the LPG includes less thanabout 0.03% volume/volume high molecular weight organic impurities. In amore particular embodiment, the LPG includes less than 10% C16.

Activated carbon is commercially available in various forms, includinggranules, powders, fibers, and the like. Activated carbon powders havegranules that are less than about 1 millimeter in size. Granularactivated carbon (GAC) sizes can be determined using known ASTM methodsand include 8×20; 20×40; 8×30 for liquid phase applications and 4×6; 4×8or 4×10 for vapor phase applications. Activated carbon can also becombined with a binder and extruded to form extruded activated carbon(EAC). Activated carbon fibers can be characterized by their length,diameter, porosity, specific surface area, and elemental composition.Length is meant to describe the distance from end to end of a fiber. Thediameter refers to the mean diameter of a fiber. Porosity ischaracterized by the mean pore volume within the fiber. Specific surfacearea is a measure of the fiber surface area, including the area withinthe pores, per unit of mass of fiber. Activated carbon fibers suitablefor use in preparing an open channel filter include activated carbonfibers having a specific surface area between about 500 to about 1300m²/g; an average diameter between about 50 nm to about 200 micron; andan average pore size between about 5 to 500 Angstroms. Pore size andmedia surface area can be measured in accordance with the teachings ofP. A. Ebb, C. Orr, Analytical Methdos in Fine Particle Technology, 1997,Micromeritics Instrument Corp. The fibers can be solid or hollow.

Preferably, the carbon media has a low capacity or no capacity (based onbreakthrough testing) for low molecular weight hydrocarbons such aspropane and butane and/or ordorant such as ethyl mercaptan.

In one embodiment, the carbon-containing filter element includes apleated media in which activated carbon (for example, granular activatedcarbon with a mesh of 20×40 or 35×60) is combined with resin and placedbetween layers of scrim. Examples of suitable resins include adhesivessuch as polyurethane (PUR) adhesive. Suitable scrim materials includepolyethersulfone (PES), polyester, or polypropylene (PP). This resultingmedia is flexible and can be pleated using known methods and used inconnection with a cartridge system.

In another embodiment, the carbon-containing filter element isconstructed as an open channel filter in which at least some of thefibers include activated carbon fiber. Methods for preparing activatedcarbon fiber are known and activated carbon fibers are commerciallyavailable. Suitable activated carbon fibers include fibers produced fromrayon, phenolics, polyacrylonitrile. Carbon fibers can be nanofibrousand/or fall into the category of nanotubes, buckytubes, nanowires, andnanohorns. These fibrous materials can be organized in any range orcombination to provide the required application performance.

In another embodiment, the carbon-containing filter element includes aformed filter in which activated carbon granules are entrapped. Suitablegranular activated carbon (GAC) include granules having a size of 8×20;20×40; or 8×30 for liquid phase applications and 4×6; 4×8 or 4×10 forvapor phase application; a surface area of at least about 500 m²/g, orbetween about 600 m²/g to about 1200 m²/g; and an average pore size ofat least about 20 Angstroms, at least about 30 Angstroms, or betweenabout 20 to 100 Angstroms.

As used herein, the term “high surface area” refers, for example, tocarbon media with a surface area of at least about 500 m²/g, or betweenabout 500 m²/g to about 2300 m²/g. The terms “open pore structure” and“macroporous” can be used interchangeably and refer to carbon media withan average pore size of at least about 20 Angstroms, at least about 30Angstroms, or between about 5 to 500 Angstroms. In some implementations,from about 20 to 100 Angstroms. Examples of macroporouscarbon-containing filter element include wood-, coconut-, or coal-basedcarbons. Pore size and media surface area can be measured in accordancewith the teachings of P. A. Ebb, C. Orr, Analytical Methdos in FineParticle Technology, 1997, Micromeritics Instrument Corp.

In another embodiment, the upstream filter element includes a nanofiberweb in which activated carbon granules are entrapped. Suitable granularactivated carbon (GAC) include granules having a size of 8×20; 20×40; or8×30 for liquid phase applications and 4×6; 4×8 or 4×10 for vapor phaseapplication; a surface area of at least about 500 m²/g, or between about600 m²/g to about 1200 m²/g; and an average pore size of at least about20 Angstroms, at least about 30 Angstroms, or between about 5 to 500Angstroms. In some implementations, average pore size is from about 20to 100 Angstroms. Suitable fibrous webs containing particulates includesthose disclosed in U.S. Pat. No. 7,655,070, which issued on Feb. 2,2010, entitled “Web Comprising Fine Fiber and Reactive, Adsorptive, orAdsorptive Particulate”, incorporated by reference in its entirety.

Downstream Filter Media

The downstream media pack has a relatively low capacity for adsorbingand retaining high molecular weight contaminants, but upon reachingcapacity it provides a restriction to flow of liquid through the mediapack. The second filter media pack (the downstream media pack) can beformed of a material comprising a fine fiber, such as nanofiber.

In one embodiment, the downstream media pack includes a web of fibers.In a more particular embodiment, the web has relatively small poresbetween the fibers, e.g., less than about 25 microns, or between about0.01 to about 25 microns, or about 0.1 to about 10 microns and, as such,provides a barrier to the passage of high molecular weight materials.The pore size measurements of the end-of-life indicator can be measuredusing methods described in An Introduction to Electrospinning andNanofibers, pages 199 to 206 (Chapter 5), Ramakrisna et al, ISBN981-256-4, 5-2, incorporated herein by reference in its entirety.

Once the upstream media pack becomes saturated, high molecular weightimpurities begin to flow through the carbon-containing filter elementdownstream to the web of fibers. Because the pores of the web are toosmall for the high molecular weight impurities to pass, the highmolecular weight impurities relatively rapidly form a film on theupstream surface of the web. The film results in an increase inbackpressure, which provides an alert that the filter needs to bechanged (end-of-life). The backpressure can be detected using a pressuredifferential sensor. Advantageously, the fiber web can also filter outcarbon particles that may be shed from the filter assembly from the LPGpermeate. If desired, one or more additional particulate filters can beincluded downstream of the filter system for the purpose of filteringout carbon particles.

In one embodiment, the fiber web includes a non-woven web ofinterlocking fibers. In a more particular embodiment, the fiber webincludes a nanofiber or microfiber polymeric web. The term “nanofiber”as used herein refers to a fiber with a diameter less than 2000nanometers or 2.0 micrometers. The term “microfiber” refers to a fiberwith a diameter larger than 2.0 microns, but less than 10 microns.Methods for forming polymeric webs are known and include processes suchas electrospinning, melt-blowing. The pore size of the web can bevaried, for example, by adjusting width of the fibers, the density ofthe fibers and thickness of the fiber layer.

Examples of suitable nanofiber materials include polymers such asnylons, polyvinylidene chloride, polyvinylidene fluoride,polyvinylalcohol (or blends thereof) such as are described in U.S. Pat.No. 6,743,273, the disclosure of which is incorporated by referenceherein. Another example of a suitable nanofiber material includespolysulfone/poly(N-vinyl lactam) alloy, such as is described in U.S.Pat. No. 7,641,055, the disclosure of which is hereby incorporated byreference herein.

FIG. 6 shows a photograph of fine fiber media that has been exposed toLPG containing high molecular weight hydrocarbons. The fine fiber mediahas accumulated deposits of high molecular weight hydrocarbonssufficient to substantially cover the media surface. This coverage,which occurs relatively rapidly (depending upon face velocity) uponexposure to high molecular weight hydrocarbons, substantially reducesflow through the media, resulting in an increased pressure differentialfrom the upstream to downstream side of the fine fiber media.

Particulate Filter

FIG. 7 is a photograph of a particulate removal media used for removalof particulates downstream from a carbon filter element, the particulateremoval media showing relatively little loading of high molecular weighthydrocarbons. Suitable particulate removal media includes, withoutlimitation, the disclosures of U.S. Pat. No. 7,314,497, entitled “FilterMedium and Structure”, and U.S. Pat. No. 7,309,372, also entitled“Filter Medium and Structure”, both of which are incorporated byreference in their entirety.

EXAMPLES

An activated carbon filter system was tested for its ability to filterhigh molecular weight organic materials from an LPG stream withoutadsorbing LPG itself.

The adsorption of propane was analyzed by measuring propane breakthroughand propane desorb. The results indicate that the activated carbons,particularly the macroporous ones, do not meaningfully adsorb propane,such that high molecular weight materials in the hexane (as an LPGsubstitute) will not have competition for absorption. Due to bindingenergy with the carbon media, high molecular weight organics will “kickoff” propane, which is only loosely bound to the carbon surface/pore.

To determine the change in relative pressure drops by the differentfilter media packs, resistance to flow was measured of various mediaafter exposure to LPG containing high molecular weight hydrocarbons. Thedeposit weight of the filter was determined by subtracting the initialweight from the final weight of the filter. FIG. 8 shows relativepressure differential by the filter media of the upstream and downstreamfilter media packs. As is indicated, the upstream media pack ofactivated carbon had a much smaller change in pressure differential thanthe downstream fine fiber media.

To determine the amount of high molecular weight hydrocarbons retainedby the filter, the filters were weighed before and after testing. Thedeposit weight of the filter was determined by subtracting the initialweight from the final weight of the filter. FIG. 9 shows relative massgain by the filter media of the upstream and downstream filter mediapacks exposed to hexane (as an LPGE substitute) and high molecularweight hydrocarbons. As is indicated, the upstream media pack ofactivated carbon had a much higher weight gain, and thus a much highercapacity.

FIG. 10 is a chart showing pressure differential in an element uponexposure to liquefied petroleum gas. In the embodiment shown, the carbonand particulate removal layers were wrapped layers (similar to theconstruction shown in FIG. 3, but with activated carbon layers andparticulate removal layers wrapped), while the end of life indicator wasa flat disk comprising nanofiber media positioned downstream from theactivated carbon layers and particulate removal layers in the axialoutlet of the filter element.

It should be noted that, as used in this specification and the appendedclaims, the singular forms “a,” “an,” and “the” include plural referentsunless the content clearly dictates otherwise. It should also be notedthat the term “or” is generally employed in its sense including “and/or”unless the content clearly dictates otherwise.

It should also be noted that, as used in this specification and theappended claims, the phrase “configured” describes a system, apparatus,or other structure that is constructed or configured to perform aparticular task or adopt a particular configuration.

The phrase “configured” can be used interchangeably with other similarphrases such as “arranged”, “arranged and configured”, “constructed andarranged”, “constructed”, “manufactured and arranged”, and the like.

All publications and patent applications in this specification areindicative of the level of ordinary skill in the art to which thisinvention pertains. All publications and patent applications are hereinincorporated by reference to the same extent as if each individualpublication or patent application was specifically and individuallyindicated by reference.

This application is intended to cover adaptations or variations of thepresent subject matter. It is to be understood that the abovedescription is intended to be illustrative, and not restrictive. Itshould be readily apparent that any one or more of the design featuresdescribed herein may be used in any combination with any particularconfiguration. With use of a molding process, such design features canbe incorporated without substantial additional manufacturing costs. Thatthe number of combinations are too numerous to describe, and the presentinvention is not limited by or to any particular illustrativecombination described herein. The scope of the present subject mattershould be determined with reference to the appended claims, along withthe full scope of equivalents to which such claims are entitled.

What is claimed is:
 1. A filter assembly for filtering high molecularweight compounds from liquefied petroleum gas, the filter assemblycomprising: a first filter media pack configured to remove highmolecular weight compounds; and a second filter media pack configured toremove high molecular weight compounds, the second filter media packlocated downstream from the first filter media pack; wherein the firstfilter media pack is configured to exhibit a change in upstream todownstream pressure differential of less than 200 percent upon reachingits functional capacity for high molecular weight compounds, and thesecond filter media pack is configured to exhibit a change in upstreamto downstream pressure differential of greater than 200 percent uponreaching saturation of high molecular weight compounds.
 2. The filterassembly of claim 1, further comprising a third media pack configured toremove solid particles from liquefied petroleum gas.
 3. The filterassembly of claim 1, further comprising a third filter media packintermediate the first filter media pack and the second filter mediapack, the third filter media pack having an mean flow pore size of 10microns or less.
 4. The filter assembly of claim 1, wherein the firstfilter media pack comprises activated carbon.
 5. The filter assembly ofclaim 4, wherein the first filter media pack comprises activated carbonhaving a surface area of at least about 500 m²/g and an average poresize of at least about 20 Angstroms.
 6. The filter assembly of claim 1wherein the second filter media pack has a total capacity for retaininghigh molecular weight hydrocarbons that is no more than 5 percent of thetotal capacity of the first filter media pack for retaining highmolecular weight hydrocarbons.
 7. The filter assembly of claim 1,wherein the first filter media pack is arranged in an open channelconfiguration.
 8. The filter assembly of claim 1, wherein the secondfilter media pack is configured to exhibit a change in upstream todownstream pressure differential of greater than 400 percent uponreaching its functional capacity of high molecular weight compounds. 9.The filter assembly of claim 1, wherein the second filter media packcomprises a fine fiber web.
 10. The filter assembly of claim 9, whereinthe second filter media pack comprises a fine fiber web with a pore sizeof no more than about 25 microns.
 11. The filter assembly of claim 9,wherein the second filter media pack comprises a fine fiber web with apore size of no more than about 10 microns.
 12. A filter assembly forfiltering high molecular weight compounds from liquefied petroleum gas,the filter assembly comprising: a first filter media pack configured toremove high molecular weight compounds, the first filter media packhaving a first total capacity for retaining high molecular weighthydrocarbons; and a second filter media pack configured to remove highmolecular weight compounds, the second filter media pack locateddownstream from the first filter media pack, the second filter mediapack having a second total capacity for retaining high molecular weighthydrocarbons; wherein the second filter media pack has a totalfunctional capacity for retaining high molecular weight hydrocarbonsthat is no more than 10 percent of the total functional capacity of thefirst filter media pack for retaining high molecular weighthydrocarbons, and wherein the second filter media pack demonstrates atleast a 25 percent increase in resistance to flow of liquefied petroleumgas upon or before reaching total capacity.
 13. The filter assembly ofclaim 12, further comprising a third media pack configured to removesolid particles from liquefied petroleum gas.
 14. The filter assembly ofclaim 12, wherein the second filter media pack has a total capacity forretaining high molecular weight hydrocarbons that is no more than 5percent of the total capacity of the first filter media pack forretaining high molecular weight hydrocarbons.
 15. The filter assembly ofclaim 12, further comprising a third filter media pack intermediate thefirst filter media pack and the second filter media pack, the thirdfilter media pack having an efficiency of at least 99.9 percent forremoval of particulate contaminants having an average particle size of 5microns.
 16. The filter assembly of claim 12, further comprising a thirdfilter media pack intermediate the first filter media pack and thesecond filter media pack, the third filter media pack having an meanflow pore size of 10 microns or less.
 17. The filter assembly of claim12, wherein the first filter media pack comprises activated carbon. 18.The filter assembly of claim 17, wherein the first filter media packcomprises activated carbon having a surface area of at least about 500m²/g and an average pore size of at least about 20 Angstroms.
 19. Thefilter assembly of claim 12, wherein the second filter media pack has atotal capacity for retaining high molecular weight hydrocarbons that isno more than 2 percent of the total capacity of the first filter mediapack for retaining high molecular weight hydrocarbons.
 20. The filterassembly of claim 12, wherein the first filter media pack is arranged inan open channel configuration.
 21. The filter assembly of claim 12,wherein the second filter media pack comprises a fine fiber web.
 22. Thefilter assembly of claim 21, wherein the second filter media packcomprises a fine fiber web with a pore size of no more than about 25microns.
 23. The filter assembly of claim 21, wherein the second filtermedia pack comprises a fine fiber web with a pore size of no more thanabout 10 microns.
 24. A filter assembly for filtering high molecularweight compounds from liquefied petroleum gas, the filter assemblycomprising: a first filter media pack configured to remove highmolecular weight compounds such that initial efficiency for removal ofhigh molecular weight hydrocarbons from a liquefied petroleum gas is atleast 80 percent at original high molecular weight hydrocarbonconcentrations of up to 0.5 percent by weight, the first filter mediapack having a first total capacity for retaining high molecular weighthydrocarbons; and a second filter media pack configured to remove highmolecular weight compounds, the second filter media pack locateddownstream from the first filter media pack, the second filter mediapack having initial efficiency for removal of high molecular weighthydrocarbons of at least 80 percent at original concentrations of up to0.5 percent by weight of the liquefied petroleum gas, the second filtermedia pack having a second total capacity for retaining high molecularweight hydrocarbons that is no more than 10 percent of the first totalcapacity of the first filter media pack; wherein the second filter mediapack demonstrates an increased resistance to flow of liquefied petroleumgas of at least 25 percent upon or before reaching total capacity. 25.The filter assembly of claim 24, further comprising a third filter mediapack intermediate the first filter media pack and the second filtermedia pack, the third filter media pack having an efficiency of at least90% percent for removal of particulate contaminants having an averageparticle size of 5 microns or higher.
 26. The filter assembly of claim24, further comprising a third filter media pack intermediate the firstfilter media pack and the second filter media pack, the third filtermedia pack having an efficiency of at least 99 percent for removal ofparticulate contaminants having an average particle size of 5 microns orhigher.
 27. The filter assembly of claim 24, further comprising a thirdfilter media pack intermediate the first filter media pack and thesecond filter media pack, the third filter media pack configured toremove particles of average particle size of 10 microns or less.
 28. Thefilter assembly of claim 24, wherein the first filter media pack forcomprises activated carbon having a surface area of at least about 500m²/g and an average pore size of at least about 20 Angstroms.
 29. Thefilter assembly of claim 28, wherein the activated carbon comprisesactivated carbon.
 30. The filter assembly of claim 24, wherein the firstfilter media pack is arranged in an open channel configuration.
 31. Thefilter assembly of claim 30, wherein the first filter media pack isarranged in an open channel configuration comprising activated carbonfiber.
 32. The filter assembly of claim 24, wherein the second filtermedia pack comprises a fine fiber web.
 33. The filter assembly of claim32, wherein the second filter media pack comprises a fine fiber web witha pore size of no more than about 25 microns.
 34. A filter assembly forfiltering high molecular weight compounds from liquefied petroleum gas,the filter assembly comprising: a first filter media pack configured toremove high molecular weight compounds such that initial efficiency ofremoving of the high molecular weight hydrocarbons is at least 80percent at initial concentrations of 5 percent and below; a secondfilter media pack configured to remove particulate contaminants, thefilter media pack configured to remove particulate contaminants locateddownstream from the filter media pack configured to remove highmolecular weight compounds, the filter media pack configured to removeparticulate contaminants and having an average pore size of no more than20 microns; an end-of-life indicator located downstream from the filtermedia pack configured to remove particulate contaminants, theend-of-life indicator comprising a fine fiber media pack with an averagepore size of no more than about 20 microns; the end-of-life indicatorhaving a increased pressure differential of 25 percent upon or beforereaching capacity.
 35. The filter assembly of claim 34, wherein thefilter media pack configured to remove high molecular weight compoundscomprises activated carbon having a surface area of at least about 500m²/g and an average pore size of at least about 20 Angstroms.
 36. Thefilter assembly of claim 35, wherein the carbon-containing filterelement comprises an open channel filter comprising activated carbonfiber.
 37. The filter assembly of claim 34, wherein the end-of-lifeindicator comprises a nanofiber or microfiber web with a pore size of nomore than about 25 microns.
 38. The filter assembly of claim 34, whereinthe filter element is generally cylindrical and at least one layer of acarbon-containing filter element is positioned outside of at least onefibrous web layer.
 39. The filter assembly of claim 34, wherein thefilter element is generally cylindrical and at least one layer of acarbon-containing filter element is positioned inside of at least onefibrous web layer.
 40. The filter assembly of claim 34, wherein theend-of-life indicator comprises a pressure indicator.
 41. The filterassembly of claim 34, wherein the end-of-life indicator comprises arefractive index meter.
 42. A method for determining service life of afilter assembly configured to remove high molecular weight hydrocarbonsfrom liquefied petroleum gas, the method comprising: providing a firstfilter media pack and passing a liquefied petroleum gas through it suchthat at least 80 percent of initial high molecular weight hydrocarbonsare removed; providing a second filter media pack located downstreamfrom the first filter media pack and passing the liquefied petroleum gasthrough it, the second filter media pack retaining at least 50 percentof remaining high molecular weight hydrocarbons; wherein the secondfilter media pack has a total capacity for retaining high molecularweight hydrocarbons that is no more than 10 percent of the totalcapacity of the first filter media pack, and wherein the second filtermedia pack demonstrates an increased resistance to flow of liquefiedpetroleum gas of at least 50 percent upon or before reaching totalcapacity.